[ruby-core:109900] [Ruby master Feature#16946] Add an `intersperse` method

["Vegard (Vegard Itland)" <noreply@ruby-lang.org>]

Issue #16946 has been updated by Vegard (Vegard Itland).


Just came across this while attempting to see if there was an elegant way to do this. My use case is that I want to generate an array with separator elements -- specifically, I want to generate a nested array of "cellable" objects in Prawn, interspersed with empty rows, for use with the `table` method. My ideal code is something like this:

``` ruby
def call(input)
  rows = input.map(&method(:to_table_row)).intersperse(empty_row)
  pdf.table(rows)
end

# dummy implementation
def to_table_row(element)
  [
    { content: "Description" },
    { content: element },
  ]
end

def empty_row
  [{ content: "", colspan: 2, borders: %i[top], height: 10 }]
end
```

Of course it's trivial to make some sort of method that does this, or just inline it, but I thought I'd pitch in with a use case :)

----------------------------------------
Feature #16946: Add an `intersperse` method
https://bugs.ruby-lang.org/issues/16946#change-99143

* Author: sos4nt (Stefan Schüßler)
* Status: Open
* Priority: Normal
----------------------------------------
Haskell has an `intersperse` function which adds a separator between elements of a list.

It would be pretty useful to have such method(s) in Ruby, too.

Examples for `Array` and `String`:
```ruby
[1, 2, 3].intersperse(0)
#=> [1, 0, 2, 0, 3]

'Hello'.intersperse('-')
#=> "H-e-l-l-o"
```

I'm aware that I can achieve the above with built-in methods, but it's quite cumbersome: (requiring regular expressions / intermediate arrays)

```ruby
[1, 2, 3].flat_map { |i| [i, 0] }[0...-1]
#=> [1, 0, 2, 0, 3]

'Hello'.gsub(/(?<=.)./, '-\0')
#=> "H-e-l-l-o"

'Hello'.chars.join('-')
#=> "H-e-l-l-o"
```




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